No Silver Lining

Swiss greenhouses predict global warming may smother plants

GLOBAL-WARMING SCENARIOS ARE MOSTLY GLOOM and doom. As humans burn more fossil fuels, more carbon dioxide (CO2) enters the atmosphere. CO2 traps the sun's heat, causing a warmer climate, rising sea levels and drastic changes in weather. The one bright spot seemed to be that because plants "breathe" CO2, they might be expected to thrive.

Not necessarily, it turns out. A study of two artificial rain forests created inside greenhouses at the University of Basel, Switzerland, indicates that too much CO2 can harm plants. One greenhouse had an atmosphere like today's; the second had as much CO2 as is predicted for...